Reducing corrosion in hydrogen production



Sept. Z9, 1964 s. M. FRANK 3,150,931

REDUCING CORROSION IN HYDROGEN PRODUCTION Filed May 1e, 1961 UnitedStates Patent O 3,156,931 REDUCHNG CRRGSIN IN HYDROGEN PRDUCTIN SidneyM. Frank, Chatham, NJ., assignor, by mesne assignments, to Pullmanincorporated, a corporation of Delaware Filed May 16, 1961, Ser'. No.110,406 6 Claims. (CCI. 2.3-213) The present invention relates to theproduction of hydrogen, and in particular, to a method for reducingcorrosion in process equipment adapted to the production of hydrogenfrom hydrocarbons.

One of the most efficient methods for producing hydrogen fromhydrocarbons involves reacting the hydrocarbon with steam and/ oroxygen, at elevated temperatures, either in the presence or absence of acatalyst, in a gas generation zone maintained under suitable conditionsto produce hydrogen and carbon monoxide, cooling the effluent of the gasgeneration zone to a lower temperature, contacting the cooled effluentin the presence of a shift conversion catalyst in a shift conversionzone maintained under suitable conditions to produce carbon dioxide andadditional hydrogen by the reaction of carbon monoxide and steam,cooling the eflluent of the shift conversion zone to condense steam,separating uncondensed materials and steam condensate, and recoveringhydrogen from the uncondensed materials. The product hydrogen is auseful raw material in a number of commercially important processesincluding, for example, the hydrogenation of unsaturated hydrocarbonsand the synthesis of methanol, hydrocarbons by Fischer-Tropsch, ammoniaand urea.

As indicated, the hydrogen process includes cooling of lthe eilluent ofthe gas generation zone before it is passed to the shift conversion zoneand cooling of the efuent of lthe shift conversion zone to condensesteam. Either or both of these two cooling steps can be carried out inwhole or in part by indirect heat exchange between the hot effluent andcooler iluids. One of the most ecient methods for carrying out at leastpart of each of these cooling steps involves circulating a portion ofthe steam condensate separated from the shift converter elhuent andinjecting it directly into .the effluent stream to be cooled.Unfortunately, however, it has been found that, regardless of the methodused to cool, the process equipment made of standard carbon steel whichis contacted by steam condensate is corroded at excessive rates. Testsindicate that the steam condensate has a relatively low pH, for example,a pH of about 5. It it postulated that carbon dioxide present in the gasis absorbed by the steam condensate to an extent suicient to render itacidic and therefore corrosive. Substitution of alloy piping andequipment having suitable resistance to corrosion constitutes anuneconomic solution to the problem.

It is therefore a principal object of the present invention to provide amethod for reducing corrosion in a system used for the production ofhydrogen.

Another object of the invention is to provide a method for renderingsteam condensed in a system used for the production of hydrogensubstantially non-corrosive, thereby permitting the use of standardcarbon steel piping and equipment in the system.

Another object of the invention is to provide a method for reducingcorrosion in a circulating condensate system used in conjunction with asystem for the production of hydrogen.

Another object of the invention is to provide a method for renderingsteam condensate, circulated in a system for the production of hydrogenfrom hydrocarbons, substantially non-corrosive, thereby permitting theuse of standard carbon steel piping and equipment in the system.

agissait Patented Sept. 29, igll ICC Various other objects andadvantages of the invention will be apparent to Ithose skilled in theart from the following detailed discussion and description.

The above objects are accomplished. in accordance with the invention bythe addition of controlled amounts of ammonia `at selected points in thesystem.

For a better understanding of the invention, reference is had to theaccompanying drawing which shows in diagrammatic for-m suitableapparatus for carrying out a preferred embodiment of the invention.Referring to the drawing, feed hydrocarbon and steam are introducedrespectively through lines 11 and 12. The combined stream in line 13 ispassed through a plurality of fired tubes 14 disposed in the radiantlsection of reformer furnace 16. The fired tubes 14 are packed withsuitable steam reforming catalyst which promotes reaction of the feedmaterials to form hydrogen and carbon monoxide. A fuel is burned, bymeans not shown, externally `of the tubes 14 in furnace 16 to providethe required heat for the endothermic reforming reaction in tubes 14.

The hot eilluent of furnace 16 containing appreciable amounts ofhydrogen and carbon monoxide is passed through line -17 to a quench drum18. Steam from line 19 and steam condensate from line 2-1 are passedthrough line 22 to distributors in drum 18. The hot reformer effluent iscooled to a temperature suitable for subsequent shift conversion bydirect contact with, and vaporization of, the quench fluid introducedthrough line 22. In addition to cooling the gas in drum 18, thecondensate-steam mixture introduced through line 22 serves to addsucient steam to the gas to provide the requirements of subsequent shiftconversion.

After the temperature of the reformer effluent is adjusted to a suitablelevel for shift conversion, it is withdrawn from drum 18 through line 23and is introduced into a shift converter 24 wherein it contacts shiftconversion catalyst which promotes the reaction of carbon monoxide andsteam to form carbon dioxide and additional hydrogen.

The effluent of shift converter 24 is withdrawn through line 26 andcooled to condense steam. As shown on the drawing, the cooling is doneby a combination of indirect heat exchange in heat exchangers 27 and 28with cooler fluids and of direct heat exchange with relatively coldcirculating steam condensate supplied through line 29. As a result ofthis cooling, the shift converter eilluent which is finally introducedinto separation drum 31 from line 32 is partially condensed. Steamcondensate is separated in drum 31, withdrawn through line 33 andrecirculated in part to lines 21 and 29 through lines 34 and 36 by meansof pump 37 to provide quenching medium.

The uncondensed material separated in drum 31 is withdrawn through line38, further cooled by indirect heat exchange with a colder fluid in heatexchanger 39 and passed to a separation drum 41. Additional steam iscondensed by this further cooling :and additional steam condensateseparates in drum 41. The latter is withdrawn in line 42, combined withthat portion of the condensate from line 33 which is in line 43 anddelivered from the process through line 44. Uncondensed materialseparated in drum 41 is withdrawn therefrom in line 46 and is deliveredfrom the process as the hydrogen-rich product. Depending upon the purityrequirements for the hydrogen produced by the process, the hydrogen-richfraction in line 46 can be used directly or after further purification.

ln order to reduce corrosion in process equipment contacted by steamcondensate, ammonia is added to the process through line 47. Thus, steamcondensed in exchanger 23 immediately absorbs ammonia from the vaporthereby rendering the condensate non-corrosive to Vrnonium carbonate orcarbamate.

the piping and equipment which it thereafter contacts.

Generally, suicient ammonia will be absorbed in the steam condensed sothat it will be unnecessary to add .further ammonia tothecondensate inany of lines 33, 34, 36, 21,'Z9`or 43 `to eflectively'reduce thecorrosivevness of such condensate, although it should be-understoodthatammonia can'be added to the condensate in any of these' lines eitherin addition to that added through line 47 or as an alternative thereto.Similarly, su-

"cient ammonia will generally be 'present in the uncondensedfractionseparated Vin drum 31 to reduce corrosion in heat exchanger '39 and theprocess equipment downstream'therefr'om contacted by additionalcondensed steam, although, again, additional ammonia can be added eitherto'line or -line 42V if necessary or desirable.

InV any case,y ammonia isV provided `at such point or points `astoinsure that all of the steam condensate is substantiallynon-corrosive tothe process equipmentwith which it comes in Contact. Ammonia can beadded as the cornpound orf'inthe form-of an aqueoussolution.

4AIt` isimportant to note thatvvhile ammonia will lbe present in theprocess illustrated either as vapor or as an aqueous solution-or -bothlthroughout the process-downstream from quench drum -18,'it is entirelyinert-in the process. Thus, it-tal es no part in any reaction-proceed--ing in shift converter Zd'nor doesit inany Way adversely Ydiscussedthus far, there is no upper limit to theamount 'of ammonia which. can beadded. However, it is preiferred to limit Vthe ammonia added toan amountsuiiicient Sto provide an ammonia concentration in the steam condensateofl about `10.to about` 1000 ppm., more usu- :ally aboutl200 toabout 300ppm. Inlthis connection,

the added ammonia should be sufficient toraise the; pH of :the steamcondensate :to a value. of about 6.5 toabout 8.5;.'preferably. about.7.0-to. about 7.5. `It is significant to note that only alimitedamount. of ammonia need be added Ato .afectfthe indicatedadjustment ofrpH. The added'ammonia doesn-not simplyA increase thesolubility -fof carbon dioxide-iny the steamcondensate so vthatunlimitedquantities.ofamrnoniawould be required. An lequilibrium is in factreached'which prevents further solution of carbon dioxide and thereby;permits raising the zsolution pH with only a very small quantity ofadded ammonia.

VAs indicated, it is, preferred to limit the amountof ammonia whichf isadded-to certain values even Ythough there is no objection toaddingjgreater -amountsfrorn the standpoint-of the process whichhas beendiscussed thus far. In instances where-.the product hydrogen in line Y46 is subjected to certain further treatment or where the v steamcondensate `in line-44 is subjected tocertain further treatment, it isquite important that. theammonia convcentrationinrthese streamsbe solimited. Forvexample,

where the hydrogen product in line 46 is treated for the separationandrecovery of carbonrdioxide in an amine absorption-stripping system toprovide arcarbon dioxide product suitable foruse in urea synthesis, verylittle arn- K monia isperrnissible in line 46. If excessive amounts ofammonia'are present-there, such ammonia may well appear in `the carbonldioxidel product which, Whencompressed to the elevated pressurerequired in urea synthesis, Vmightbe accompanied with precipitation ofarn- In connection with the steam condensate recovered in line .44, thisexcess condensate is frequently supplied to the deaerator and boiler ofthe plant steam generating system. Such systems frequently include brassand bronze parts which are susceptible to corrosion by alkalinesolution. While the deaerator will remove at least some ammonia, it maynot be able to remove suicient ammonia in cases where the steamcondensate in line 4d has an unduly high pH. Thus, in either of thesecircumstances, it is important to limit the amount of ammonia added tothe circulating condensate system to values within the preferred rangesmentioned in order to avoid the problems discussed.

The hydrocarbon gasification process used can be any one of many whichare welllrnown in the art. Thus, while catalytic steam reforming infired tubes is shown Yin theldrawing and is preferred, the .hydrocarboncanralso be Vgasiii'ed by partial oxidation with substantiallyA pureoxygen or by a combination of catalytic steamreforming and such partialoxidationinheated or adiabatic apparatus, Conditions used in eachofthese gasification processes are well known and are therefore notdiscussed further here. Similarly, suitable catalysts and conditions`for shift conversion are well known and therefore reconversion.Accordingly, it will be useful in all such processes to practice aquenching operation on theeilluent such as is done inY quench drum 18;of theV specific process illustrated inthe drawing. `Suitableinlettemvperatures for the shiftconversion zone include Values of about`v600 to about 800 F.,y preferably about 650 to about 750 F. Thus,suihcient condensate is usedas 'quench' toreduce' the temperature ofltheA eluent of 7 the gas generation zone to a temperature in thisrange.

Where vaporization of condensate provides insuicient circulatedcondensate. lthe process requireheat atlevels available inthe etiiuent-of the shift converter, then itiswadvantageous todo some steam tomeetrequirements of shift conversion, Vsteam can also be supplied' alongwith the condensate to satisfy the requirements. In connection withcooling -the eiiuent-of the shift conversion zonefit should beunderstood that all of the cooling done can be "done by injectingHowever, where otherparts of or all of the cooling in indirect heatexchangers as shown.

`rIrl-'any case,steam is condensed and, accordingly, the

method of the present invention is applicable.

Asa specific example of the present invention, a' prodvu'ctcontainingabout74.7 mol'percent-Ahydrogen, on a drawing. The desulphurized naturalgas fed in line 11 j andY about 118 p.s.i.g. wasV cooled in heatexchanger`27 to about 65 8f F. by indirect heat exchange v'vith arcoolerat about F. and about 170 p.s.i.g., Wasrcombined with about 18,610,1bs.per hour of steam at about -p.s.i.g. and about 485 F. The combined-feedin line 13.at'about 350'F. was contacted intheY presence of astandard commercial nickel reforming catalystV in tubes v14 ofreforrnerfurnace 16. The ellluentlof furnace 16 Vin line 17 at about 1545 F. andabout 125 psig. was

contacted in quench drum 18 With about 9,630 lbs.Y per hour of steamfrom line 19 and about 775 barrels per stream day (b.p.s.d.) of steamcondensate from line'21 lwhich together were introduced through line 22.The

cooled reformer eiiluent in line 23 at about 650 F. was

' passed over two iiXred-,beds of standard commercialciron oxide shiftconversion catalyst in shift converter24. The efliuent of shiftconverter 24 in line 26 at about (750. F

iiuid. vTheshift converter eiiluent was further cooled to about 305 F.bythe injection of about 708 b.p.s.d. of

steam condensate through line 29. In heat exchanger 28, the eiiiuent wasstill further cooled and was partially condensed at a temperature ofabout 260 F. by indirect heat exchange with a colder fluid. About 2070b.p.s.d.

of steam condensate at 260 F. was separated in drum 5 31 and withdrawnthrough line 33. Of this steam condensate, about 1483 b.p.s.d. wasdiverted through line 34 and passed by pump 37 through line 36 to lines21 and 29 to provide quench. Uncondensed materials were withdrawn fromdrum 31 through line 38, cooled to about lo 115 F. in heat exchanger 39by indirect heat exchange with cooling water and passed to separationdrum 41. About 850 b.p.s.d. of additional steam condensate was separatedin drum 41 and withdrawn through line 42, combined with about 587b.p.s.d. of condensate in line 43 and together passed at a combinedtemperature of about 174 F. to the plant boiler house for steamgeneration. The hydrogen-rich product of the process separated in drum41 as uncondensed material was withdrawn from the process through line46. In this particular in 20 stance, the product was further treated inan amine absorption-stripping system -to separate substantially purecarbon dioxide for use in urea synthetisis and substantially purehydrogen for use in ammonia synthesis.

On start-up of the foregoing plant, there occurred excessive corrosionof process equipment coming into contact with steam condensate. Thelatter was tested and found to have a pH of about 5.2. After theprovision of line 47 through which about 3.5 lbs. of ammonia per hourwere added, it was found that the corrosion rate was appreciably reducedin the steam condensate system. Hence, it was economically feasible tomaintain ordinary carbon steel process equipment in the system and avoidthe great expense of replacing such equipment with stainless steel.

TABLE Composition of Principal Streams, Mols/Hr.

Component 11 17 26 46 40 It should be apparent that many modificationscan readily be made by those skilled in the art in the foregoing processwithout departing from the scope of the invention. Thus, for example, itis apparent that the particular sequence of indirect heat exchange,direct heat exchange and indirect heat exchange of the shift convertereffluent in line 26 can be varied to suit particular process situations.Similarly, steam can be condensed and separated in a single stage or inthree or more stages rather than the two stages specifically described.It is apparent that the circulated condensate can be furnished entirelyfrom a lower temperature stage of condensate separation or from acombination of low and high temperature stages rather than entirely fromthe high temperature stage specifically described. These examples aremerely illustrative of some of the various changes which can be madewithout departing from the scope of the present invention.

I claim:

1. In a process for the production of hydrogen comprising contacting agas containing carbon monoxide with steam in a shift conversion zonemaintained under suitable conditions to produce hydrogen and carbondioxide, and cooling the eiiiuent of the shift conversion zone tocondense steam, the improvement for reducing corrosion in processequipment contacted by steam condensate which comprises adding ammoniato said process at a point upstream from where steam condenses -in anamount sufficient to adjust the -pH of said steam condensate to a valueof about 6.5 to about 8.5.

2. In a process for the production of hydrogen comprising contacting agas containing carbon. monoxide with steam in a shift conversion zonemaintained under suitable conditions to produce hydrogen and carbondioxide, cooling the effluent of the shift conversion zone to condensesteam, separating uncondensed materials and steam condensate,withdrawing said uncondensed materials as hydrogen product, andinjecting at least a portion of said separated steam condensate into theeffluent of said shift conversion zone to achieve at least a part of theaforesaid cooling thereof, the improvement for reducing corrosion inprocess equipment contacted by steam condensate which comprises addingammonia to said process in an amount sutcient to adjust the pH of saidsteam condensate to a value of about 6.5 to about 8.5.

3. In a process for the production of hydrogen comprising gasifying ahydrocarbon in a gas generation zone to produce hydrogen and carbonmonoxide, cooling the effluent of the gas generation zone, contactingcooled efiiuent of the gas generation zone with steam in a shiftconversion zone maintained under suitable conditions t0 produce carbondioxide and additional hydrogen by reaction of carbon monoxide withsteam, cooling the effluent of the shift conversion zone to condensesteam, separating uncondensed materials and steam condensate,withdrawing said uncondensed materials as hydrogen product, andinjecting at least a portion of said separated steam condensate into atleast one of said effluents to achieve at least a part of the aforesaidcooling thereof, the improvement for reducing corrosion in processequipment contacted by steam condensate which comprises adding ammoniato said process in an amount sufficient to adjust the pH of said steamcondensate to a value of about 6.5 to about 8.5.

4. In a process for the production of hydrogen comprising gasifying ahydrocarbon in a gas generation zone to produce hydrogen and carbonmonoxide, cooling the effluent of the gas generation zone, contactingcooled effluent of the gas generation zone with steam in a shift con-Version zone maintained under suitable conditions to produce carbondioxide and additional hydrogen by reaction of carbon monoxide withsteam, cooling the efuent of the shift conversion zone to condensesteam, separating uncondensed materials and steam condensate,withdrawing said uncondensed materials as hydrogen product, andinjecting at least a portion of said separated steam condensate into theeiuent of the gas generation zone to achieve at least a part of theaforesaid cooling thereof, the improvement for reducing corrosion inprocess equipment contacted by steam condensate which comprises addingammonia to said process in an amount suicient to adjust the pH of saidsteam condensate to a value of about 6.5 to about 8.5

5. In a process for the production of hydrogen comprising contacting ahydrocarbon with steam in the presence of a reforming catalyst in areforming zone maintained under suitable conditions to produce hydrogenand carbon monoxide, cooling the eiuent of the reforming zone to atemperature between about 600 and about 800 F., contacting cooledeifluent from the reforming zone with steam in the presence of a shiftconversion catalyst in a shift conversion zone maintained under suitableconditions to produce carbon dioxide and additional hydrogen by reactionof carbon monoxide and steam, cooling the efliuent of the shiftconversion zone to a temperature below its dewpoint, separatinguncondensed materials and steam condensate, withdrawing uncondensedmaterials as hydrogen product, and injecting at least a portion of saidseparated steam condensate into at least one of said ef- :the/reef, ytheimprqyemegt'-fQrQredcing orfosiqnin' process equipment conf@ by Steamcndensate which'com- 8 `V:1711 f lthe cbling rec'itedf for theefent 0fSaid reforming z'ne.V

l Referenrsf Cfasin Heime -f-his "patent UNITED STATES 'Y PATENTS

1. IN A PROCESS FOR THE PRODUCTION OF HYDROGEN COMPRISING CONTACTING AGAS CONTAINING CARBON MONOXIDE WITH STEAM IN A SHIFT CONVERSION ZONEMAINTAINED UNDER SUITABLE CONDITINS TO PRODUCE HYDROGEN AND CARBONDIOXIDE, AND COOLING THE EFFLUENT OF THE SHIFT CONVERSION ZONE TOCONDENSE STEAM, THE IMPROVEMENT FOR REDUCING CORROSION IN PROCESSEQUIPMENT CONTACTED BY STEAM CONDENSATE WHICH COMPRISES ADDING AMMONIATO SAID PROCESS AT A POINT UPSTREAM FROM WHERE STEAM CONDENSES IN ANAMOUNT SUFFICIENT TO ADJUST THE PH OF SAID STEAM CONDENSATE TO A VALUEOF ABOUT 6.5 TO ABOUT 8.5.